1. Field of the Invention
The present invention relates to an ink-jet printer, and more particularly to a drive roller releasing apparatus for the ink-jet printer that prevents curling of print material being produced by a drive roller assembly during printing.
2. Description of the Related Art
Generally, a printer connected to a computer makes copies of document or other information held by the computer on print materials. There are various types of printers, such as laser printers or ink-jet printers. The ink-jet printer electrostatically sprays ink from a nozzle onto a print material, such as paper, and prints document or information held by the computer onto the print materials.
Referring to FIG. 1, a conventional ink-jet printer comprises a pick-up roller 10, a drive roller assembly 20, a feed roller 30, a printing unit 40, and a discharge roller 50. The pick-up roller 10 separates one print material 1 from the other print materials stacked within a printing material cassette 11, and moves the print material 1 into the drive roller assembly 20. The drive roller assembly 20 moves the print material 1 transferred from the pick-up roller 10.
Referring to FIGS. 1, 2 and 3, the drive roller assembly 20 includes a pinch roller 24, a pinch spring 26, a drive roller 21, a gear train 27, and a drive motor 28. The pinch roller 24 is parallel with the drive roller 21 and is pressed against the drive roller 21 by the pinch spring 26. A drive gear 23 is co-axially disposed at one end of the drive roller 21, and meshes with the gear train 27. The drive motor 28 is disposed on a frame 29 mounted in a body of the ink-jet printer. A pinion 28a, which meshes with the gear train 27, is disposed at a shaft of the drive motor 28. The feed roller 30 feeds the print material 1 transferred from the drive roller assembly 20 to be below the printing unit 40. The printing unit 40 prints on the print material 1 fed from the feed roller 30. The discharge roller 50 discharges the print material 1 on which information is printed by the printing unit 40.
In the ink-jet printer constructed as above, an operation of printing is described below referring to FIGS. 1 to 2. The print material 1 is separated from the printing material cassette 11 and is moved into the drive roller assembly 20 by the pick-up roller 10. The print material 1 transferred by the pick-up roller 10 is moved into a gap between the drive roller 21 and the pinch roller 24 of the drive roller assembly 20, and is then moved into the feed roller 30 by a friction force caused by a pressure between the drive roller 21 and the pinch roller 24. The feed roller 30 feeds the print material 1 transferred from the drive roller assembly 20 for predetermined lengths of the print material 1 and intervals to a printing head of the printing unit 40. Then, for each predetermine length of the print material 1, the printing head, moving from side to side, prints information onto the print material 1 fed by the feed roller 30. After printing on the predetermined length of the print material 1 is completed, the printing material 1 is again fed for the predetermined length to be below the printing unit 40 using the drive roller assembly 20 and the feed roller 30. If printing on the total length of the print material 1 is completed through the procedure described above, the printed print material 1 is discharged by the discharge roller 50. The predetermined length discussed above is determined in accordance with the printing head's size.
However, the ink-jet printer printing through the above-described procedure has a problem that the images printed on the print material are inferior. This problem is due to a band feed accuracy not being good when the feed roller 30 feeds the print material 1 at the predetermined length to be below the printing unit 40.
Referring to FIGS. 3 and 4, the reason of bad band feed accuracy is described as follows. When a front end of the print material 1 transferred by the pick-up roller 10 is moved into the gap between the drive roller 21 and the pinch roller 24, the drive roller 21 is rotated clockwise by the drive motor 28. As the drive roller 21 is rotated, the print material 1 is moved to the feed roller 30 by the friction force that is caused by the pressure force of the pinch spring 26 pressing the pinch roller 24 against the drive roller 21. The front end of the print material 1 passed by the drive roller assembly 20 is guided by first and second printing material guides 32,34, and is thus moved into the feed roller 30. If the front end the print material 1 is moved into the feed roller 30, the feed roller 30 and the drive roller 21, which are synchronously controlled by a controller (not shown), feed the printing material 1 at the predetermined length to the to be below the printing head of the printing unit 40.
At this time, the portion print material 1 between the drive roller 21 and the feed roller 30 has a curl 1′ formed during the guidance by the first and second printing material guides 32, 34 as shown in FIG. 4. Because each of the drive roller 21 and the feed roller 30 feeds the printing material 1 with the same speed, the curl 1′ is maintained until a back end of the print material 1 is leaves the drive roller 21.
Because the front end of the print material 1 is pushed in the feed roller's direction by a force caused by a spring back effect of the curl 1′, the printing material 1 is fed beyond the predetermined length. But when the back end of the printing material 1 leaves the drive roller 21, the curl 1′ disappears, and the force, which otherwise pushes the print material 1 in the feed roller's direction, vanishes. Therefore, the printing material 1 is fed by the feed roller 30 by exactly predetermined length. In other words, during the printing for the total length of the print material 1, a feed length moved by the feed roller 30 while the printing material has the curl 1′ is different from a feed length moved by the feed roller 30 while the print material 1 does not have the curl 1′. Accordingly, the band feed accuracy of the print material 1 by the feed roller 30 deteriorates. When the band accuracy of the printing material deteriorates, the print quality consequently deteriorates.